"Double-byte enabled" is very different from "Unicode enabled". The former
refers to apps that can navigate, maybe edit, and display DBCS text such as
Shift-JIS. Typically the ASCII characters in a DBCS character repertoire
are represented by single bytes and most, if not all, other characters are
represented by a lead byte followed by a trail byte. So you have a mix of
single and double byte characters. It gets particularly tricky, since some
lead bytes can also be trail bytes. Accordingly if you land in the middle
of the text it can be tricky to figure out where a character boundary is
(finding it used to be a favorite interview question at Microsoft).

In your document, it would be better to say something about making sure
applications are Unicode enabled. Double-byte enabling used to be
desirable, but now it should only be needed for import/export code.